Fuel injectors often have piece-to-piece and time-to-time variability, due to imperfect manufacturing processes and/or injector aging (e.g., clogging), for example. This injector variability may cause cylinder torque output imbalance due to the different amount of fuel injected into each cylinder, and may also cause higher tail pipe emission and reduced fuel economy due to an inability to correctly meter the fuel to be injected into each cylinder.
U.S. Pat. No. 7,841,319 discloses methods of characterizing the operation of direct injection fuel injectors and mitigating inaccuracy in fuel injection. In particular, deactivation of a fuel pump may be followed by commanding a fuel injector to inject a given fuel quantity. Based on the resulting pressure drop in the fuel rail, the actual fuel quantity injected is computed. By comparing the commanded fuel quantity to the actual fuel quantity injected, fuel injector operation may be diagnosed and/or compensated to mitigate inaccuracy in fuel metering.
The inventors herein have identified an issue with the above approach. Specifically, sampling of fuel rail pressures in the crank angle domain is performed. As such, other tasks are also performed in the crank angle domain, such as filtering. As these actions are performed on an event basis, they yield additional computational cost and complexity relative to analogous actions that may be performed in the time domain. These issues are exacerbated by the effort expended to reconcile crank angle actions with time domain actions.
One approach that at least partially addresses the above issues includes a method of characterizing fuel injector operation, comprising determining a flow error of a single fuel injector of two or more fuel injectors positioned in a first fuel rail by comparing a sum of each of a plurality of injector commands for the single injector to a fuel amount pumped into the first fuel rail, the fuel amount being predetermined.
In a more specific example, each of the plurality of injections is performed between successive full pump strokes performed by a fuel pump, the fuel pump supplying fuel to the two or more fuel injectors in the first fuel rail.
In another aspect of the example, each of the plurality of injections occurs after the fuel pump has performed a full pump stroke and pumping by the fuel pump following the full pump stroke has been suppressed.
In this way, the operation of fuel injectors may be individually characterized and specific fuel injectors flow errors compensated, increasing fuel metering accuracy. Thus, the technical result is achieved by these actions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.